Invasive swamp rodent has California scrambling to come up with a battle plan

How to tell an invasive swamp rodent from other California critters

An infestation of nutria, an invasive swamp rodent, was recently found in the Sacramento-San Joaquin Delta. See how to identify them and report sightings.
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An infestation of nutria, an invasive swamp rodent, was recently found in the Sacramento-San Joaquin Delta. See how to identify them and report sightings.
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Gustine, Merced County

About the size of a beagle, they can quickly turn a lush green marsh to a wasteland. They use their long orange teeth to gnaw through vegetation and reach the succulent bits they crave.

Females can have litters of a dozen or more and become pregnant within 48 hours after giving birth, their fertility adding to the speed with which this South American rodent can fan across a landscape, burrowing into levees and and destroying wetlands along the way.

They are called nutria, and right now they’re starting to spread through the waterways leading into the Sacramento-San Joaquin Delta, the ecologically fragile network of sloughs and rivers that functions as the heart of California’s flood-control and water distribution system. The first ones were discovered last year in Merced County. Since then, at least two dozen more have been found there and in Stanislaus, Tuolumne and Fresno counties.

No one knows how they got here, or just how many there are. It’s illegal to import nutria into California.

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The nutria is an invasive rodent that has recently been discovered in rivers and wetlands near Modesto and Merced. California officials hope to eradicate them before they can become established.

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Officials at California’s wildlife agency say they know they need to act fast to stop a major infestation. Within five years, the state estimates nearly a quarter million nutria could be chewing their way through what’s left of the state’s wetlands and digging holes in California’s vast network of irrigation canals and flood-control levees.

In other states, taxpayers have spent tens of millions of dollars fighting nutria infestations.

But so far, California’s efforts consist mainly of Greg Gerstenberg, a lone state biologist in Los Banos who is trapping nutria on a few acres of a private duck hunting marsh in Gustine, Merced County, where they were first discovered.

One day in February, Gerstenberg slogged through the water flooding the marsh in chest waders to check his nine traps. They were empty, though it was obvious that some of them had been visited. The sweet potatoes he had set out to bait the traps had teeth marks, but the traps never triggered.

The biologist has managed to catch and kill around 20 nutria since last year. Once an animal is trapped, he shoots it in the head with a .22 caliber rifle. Gerstenberg says he suspects he’s barely making a dent in the population, and he practically begged for help.

“This animal needs to be controlled now,” he said. “We have a limited window of opportunity here.”

A “Nutria Response Team” has been set up in recent months to tackle the state’s infestation. It includes the U.S. Department of Agriculture and the U.S. Fish and Wildlife Service, along with state and local agriculture, water and wildlife officials.

The team is preparing an eradication plan. It’s also scrambling to secure funds for an all-out nutria assault, but progress is slow. Assembly Bill 2470, authored by Timothy Grayson, D-Concord, would set aside $10 million in state funds for an invasive species program. The legislation was only just introduced.

California Department of Fish and Wildlife Senior Environmental Scientist Valerie Cook Fletcher wades through wetlands near Gustine in search of nutria, a large aquatic South American rodent between the size of a muskrat and a beaver, that pose a serious environmental threat to the estuary because their destructive feeding and burrowing habits.
Randall Benton
rbenton@sacbee.com

“The biggest impediment to eradicating the nutria threat is adequate funding,” California Department of Fish and Wildlife spokesman Peter Tira said in an emailed statement. “There is limited funding available to marshal the necessary people and resources to remove nutria from the landscape. We’re in the process now of selecting the best tools and means available to get the job done with the funds we do have and working to identify additional funding.”

One potentially controversial question facing the state Department of Fish and Wildlife as it crafts its nutria battle plan is whether to turn to the entity with the most proven nutria killing credentials: Wildlife Services, the animal-extermination wing of the U.S. Department of Agriculture.

The agency is so fiercely despised by environmental and animal-welfare groups that some state officials hesitate to even discuss the possibility.

Valerie Cook Fletcher, a supervisor at the state Department of Fish and Wildlife’s invasive species program, paused for several seconds and answered slowly and cautiously when asked whether her department was going to seek help from Wildlife Services to attack the nutria infestation.

“The department has sensitivity around working with Wildlife Services,” she said earlier this month while touring the Merced wetlands with Gerstenberg.

Wildlife Services employs specialized exterminators to kill nuisance wild animals across the US. The agency is credited with eliminating the decades-old nutria infestation in the Chesapeake Bay on the East Coast. Using specially trained nutria-sniffing dogs, traps and other methods, it killed more than 14,000 nutria that had infested the bay. The program was so successful, not a single nutria has been spotted for more than two years.

“They’ve done an effective job in the Chesapeake,” Cook Fletcher said. “It’s their area of expertise. They have the equipment.”

But in California, animal rights activists and environmental groups hold considerable sway over state wildlife policy, and they despise what they call the “killing agency.” They accuse Wildlife Services of engaging in decades of needless slaughter of wild animals, usually on behalf of agricultural clients. A Sacramento Bee investigation in 2012 revealed that since 2000, Wildlife Services employees had killed nearly a million coyotes, millions of birds, from nonnative starlings to migratory shorebirds, and more than 300 other species, including black bears, beavers, porcupines, river otters, mountain lions and wolves.

Wildlife Services has been sued repeatedly over the years. Just recently, five wildlife protection groups, including the Center for Biological Diversity and Project Coyote, declared a victory when a federal judge signed off on a settlement that banned Wildlife Services from trapping and using aerial gunning in designated Northern California wilderness areas.

Brooks Fahy, director of Predator Defense, one of Wildlife Services’ most ardent critics, said the agency routinely violates state and federal wildlife laws, and is notoriously secretive. The Bee investigation used agency data to highlight how thousands of animals that have ended up in Wildlife Services’ traps weren’t the ones the agency was targeting for extermination. That sometimes includes animals inadvertently caught when the agency targets nutria, Fahy said. He cited a 2011 case in Oregon in which the agency’s nutria trap snared and strangled a family’s border collie.

“I don’t think the state of California should be doing business with Wildlife Services at all,” Fahy said. “I don’t think any state should.”

Wildlife Services is part of the multi-agency team crafting a nutria response plan for California. Officials there declined an interview with The Bee to talk about its possible role.

In an emailed statement, USDA spokeswoman Tanya Espinosa said Wildlife Services is “currently collaborating with the State of California on this issue.” The agency pointed to its success eliminating nutria from the Chesapeake Bay.

“While there was occasionally some resistance to the removal of nutria in the Chesapeake Bay area, the majority of the residents here also realized that the removal was necessary ... to ensure a healthy and balanced ecosystem and environment,” Espinosa said.

Wildlife Services has its supporters in California, particularly among agricultural groups. They argue that the agency is unfairly attacked, and that it has evolved greatly over the years, now working with land owners on preventative measures before deciding to kill problem animals.

When it comes to eradicating nutria, the agency “knows what they’re doing,” said Noelle Cremers of the California Farm Bureau Federation. “The Chesapeake Bay example shows that they have that expertise.”

Until the state decides how to respond to the nutria threat, Gerstenberg is doing what he can to hold the population in check. He relies on cages that capture animals live so they can be released unharmed if they nab the wrong species. The biologist said there are more effective trapping methods, but he’s banned from using them under California law. Proposition 4, passed in 1998, banned “body-gripping” and leg-hold traps, neck snares and certain poisons because they were deemed inhumane. There are no loopholes in the ballot initiative for setting out the more effective traps for a rapidly expanding nutria infestation.

Senior Environmental Scientist Valerie Cook Fletcher and Senior Wildlife Biologist Greg Gerstenberg of the California Department of Fish and Wildlife check a trap for nutria near Gustine. A large aquatic South American rodent between the size of a muskrat and a beaver, nutria have been found in the Sacramento-San Joaquin Delta and pose a serious environmental threat to the estuary because their destructive feeding and burrowing habits.
Randall Benton
rbenton@sacbee.com

Even a small tweak to the language of the law would require going back to voters. That’s a costly and time-consuming process with no guarantee of success.

For now, the state wildlife agency is focusing on public awareness and urging citizens to report any nutria sightings. It is spreading the word about the grave threat nutria pose to the Central Valley’s network of canals, sloughs and levees, which are often connected to wildlife refuges and private marshlands, and the possibility that they will migrate into the delta, which supplies water to millions of acres of farmland and 25 million Californians.

Nutria can grow to more than 20 pounds. Notoriously destructive feeders, a colony can rip apart acres and acres of native marsh plants in a short amount of time. As they make dens, they can burrow through flood-protection levees and undermine their foundations.

Originally brought to North America for fur farming, these prolific rodents can spread through non-native habitats with remarkable speed. Once they get established, they’re almost impossible to eliminate. Louisiana, for instance, spends more than $1 million each year paying hunters and trappers in a bounty program, but the killing is only keeping the population in check – not eliminating it.

The reason is because nutria are incredibly prolific. A female nutria becomes sexually mature in as little as four months and can have a litter of a dozen or more. A female’s teats sit high on her flanks, nearly along her spine. This allows her to nurse while she floats in the water.

Their offspring quickly disperse. The youngsters have been known to strike out 50 miles or more in search of new territory.

The thought of nutria expanding across the Central Valley’s interconnected network of canals and sloughs into wetland habitats is a shudder-inducing prospect for California wildlife officials. More than 90 percent of the state’s wetlands – home to numerous threatened and endangered fish, birds, reptiles and mammals – have been plowed or paved over. What’s left is precious.

Given what’s at stake, even some of Wildlife Services’ most ardent critics aren’t outright opposed to the agency handling California’s infestation.

Collette Adkins, a senior attorney for the Center for Biological Diversity, said her group’s opposition to the agency stems from its killing of native wildlife, especially apex predators such as coyotes and wolves. She said her group – among the most litigious in the environmental community – isn’t likely to oppose Wildlife Services if it puts the nutria in its sights.

“We just hope they can use methods that are as humane as possible,” Adkins said.